GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc1085

Network Working Group M. Rose Request for Comments: 1085 TWG

                                                         December 1988
                     ISO Presentation Services
                  on top of TCP/IP-based internets

Status of this Memo

 This memo proposes a standard for the Internet community.
 Distribution of this memo is unlimited.

1. Introduction

 [RFC1006] describes a mechanism for providing the ISO transport
 service on top of the Transmission Control Protocol (TCP) [RFC793]
 and Internet Protocol (IP) [RFC791].  Once this method is applied,
 one may implement "real" ISO applications on top of TCP/IP-based
 internets, by simply implementing OSI session, presentation, and
 application services on top of the transport service access point
 which is provided on top of the TCP.  Although straight-forward,
 there are some environments in which the richness provided by the OSI
 application layer is desired, but it is nonetheless impractical to
 implement the underlying OSI infrastructure (i.e., the presentation,
 session, and transport services on top of the TCP).  This memo
 describes an approach for providing "stream-lined" support of OSI
 application services on top of TCP/IP-based internets for such
 constrained environments.

2. Terminology

 In as much as this memo is concerned primarily with concepts defined
 in the framework of Open Systems Interconnection (OSI) as promulgated
 by the International Organization for Standardization (ISO), the
 terminology used herein is intended to be entirely consistent within
 that domain of discourse.  This perspective is being taken despite
 the expressed intent of implementing the mechanism proposed by this
 memo in the Internet and other TCP/IP-based internets.  For those
 more familiar with the terminology used in this latter domain, the
 author is apologetic but unyielding.
 Although no substitute for the "correct" definitions given in the
 appropriate ISO documents, here is a short summary of the terms used
 herein.

Rose [Page 1] RFC 1085 ISO Presentation Services December 1988

    Application Context:
       The collection of application service elements which
       cooperatively interact within an application-entity.
    Application Service Element:
       A standardized mechanism, defined by both a service and a
       protocol, which provides a well-defined capability, e.g.,
       ROSE -  the Remote Operations Service Element,
               which orchestrates the invocation of "total"
               operations between application-entities [ISO9066/2].
       ACSE -  the Association Control Service Element,
               which manages associations between application
               entities [ISO8650].
    Object Identifier:
       An ordered set of integers, used for authoritative
       identification.
    Presentation Service:
       A set of facilities used to manage a connection between two
       application-entities.  The fundamental responsibility of the
       presentation service is to maintain transfer syntaxes which
       are used to serialize application protocol data units for
       transmission on the network and subsequent de-serialization
       for reception.
    Protocol Data Unit (PDU):
       A data object exchanged between service providers.
    Serialization:
       The process of applying an abstract transfer notation to an
       object described using abstract syntax notation one (ASN.1)
       [ISO8824] in order to produce a stream of octets.
       De-serialization is the inverse process.
       It is assumed that the reader is familiar with terminology
       pertaining to the reference model [ISO7498], to the service
       conventions in the model [ISO8509], and to the
       connection-oriented presentation service [ISO8822].

3. Scope

 The mechanism proposed by this memo is targeted for a particular
 class of OSI applications, namely those entities whose application
 context contains only an Association Control Service Element (ACSE)
 and a Remote Operations Service Element (ROSE).  In addition, a

Rose [Page 2] RFC 1085 ISO Presentation Services December 1988

 Directory Services Element (DSE) is assumed for use by the
 application-entity, but only in a very limited sense.  The
 organization of such an entity is as follows:
    +------------------------------------------------------------+
    |                                                            |
    |                     Application-Entity                     |
    |                                                            |
    |    +------+              +------+              +------+    |
    |    | ACSE |              | ROSE |              | DSE  |    |
    |    +------+              +------+              +------+    |
    |                                                            |
    +------------------------------------------------------------+
    |                                                            |
    |                Presentation Services                       |
    |                                                            |
    |    P-CONNECT         P-RELEASE         P-DATA              |
    |                      P-U-ABORT                             |
    |                      P-P-ABORT                             |
    |                                                            |
    +------------------------------------------------------------+
 The mechanism proposed by this memo is not applicable to entities
 whose application context is more extensive (e.g., contains a
 Reliable Transfer Service Element).  The mechanism proposed by this
 memo could be modified to support additional elements.  However, such
 extensions would, at this time, merely serve to defeat the purpose of
 providing the minimal software infrastructure required to run the
 majority of OSI applications.
 The motivation for this memo was initially derived from a requirement
 to run the ISO Common Management Information Protocol (CMIP) in
 TCP/IP-based internets.  In its current definition, CMIP uses
 precisely the application service elements provided for herein.  It
 may be desirable to offer CMIP users a quality of service different
 than the one offered by a connection with a high-quality level of
 reliability.  This would permit a reduced utilization of connection-
 related resources.  This memo proposes a mechanism to implement this
 less robust -- and less costly -- quality of service.

4. Approach

 The approach proposed by this memo relies on the following
 architectural nuances:

Rose [Page 3] RFC 1085 ISO Presentation Services December 1988

  1. the TCP is a stream-oriented transport protocol
  1. ASN.1 objects, when represented as a stream of octets are

self-delimiting

  1. The ISO presentation service permits the exchange of ASN.1

objects

  1. The ACSE and ROSE require the following presentation

facilities:

         The Connection Establishment Facility
         The Connection Termination Facility
         The Information Transfer Facility (P-DATA
         service only)
  1. The majority of the parameters used by the services which

provide these facilities can be "hard-wired" to avoid

     negotiation
 In principle, these nuances suggest that a "cheap" emulation of the
 ISO presentation services could be implemented by simply serializing
 ASN.1 objects over a TCP connection.  This approach is precisely what
 is proposed by this memo.
 Given this perspective, this memo details how the essential features
 of the ISO presentation service may be maintained while using a
 protocol entirely different from the one given in [ISO8823]. The
 overall composition proposed by this memo is as follows:
 +-----------+                                       +-----------+
 |  PS-user  |                                       |  PS-user  |
 +-----------+                                       +-----------+
      |                                                     |
      | PS interface                           PS interface |
      |  [ISO8822]                                          |
      |                                                     |
 +----------+   ISO Presentation Services on the TCP  +----------+
 |  client  |-----------------------------------------|  server  |
 +----------+              (this memo)                +----------+
      |                                                     |
      | TCP interface                         TCP interface |
      |  [RFC793]                                           |
      |                                                     |

Rose [Page 4] RFC 1085 ISO Presentation Services December 1988

 In greater detail, the "client" and "server" boxes implement the
 protocol described in this memo.  Each box contains three modules:
  1. a dispatch module, which provides the presentation services

interface,

  1. a serialization module, containing a serializer, which takes

an ASN.1 object and applies the encoding rules of [ISO8825]

      to produce a stream of octets, and a de-serializer, which
      performs the inverse operation, and
  1. a network module, which manages a TCP connection.
 The software architecture used to model a network entity using this
 approach is as follows:
 +---------+    +----------+                                   +-----+
 |         |    |          |  output +---------------+  input  |  n  |
 |         |    |          |<--------| de-serializer |<--------|  e  |
 |         |    |          |   queue +---------------+  queue  |  t  |
 | PS-user |----| dispatch |                                   |  w  |
 |         |    |          |  input  +---------------+ output  |  o  |
 |         |    |          |-------->|   serializer  |-------->|  r  |
 |         |    |          |  queue  +---------------+ queue   |  k  |
 +---------+    +----------+                                   +-----+
                               |---- serialization module ----|
 The ISO presentation layer is concerned primarily with the
 negotiation of transfer syntaxes in addition to the transformation to
 and from transfer syntax.  However, using the mechanism proposed by
 this memo, no negotiation component will be employed.  This memo
 specifies the fixed contexts which exist over each presentation
 connection offered.  This memo further specifies other constants
 which are used in order to eliminate the need for presentation layer
 negotiation.

5. Fundamental Parameters

 There are certain parameters which are used by the presentation
 service and are defined here.
    1. Presentation address:
    The structure of a presentation address is presented in Addendum 3
    to [ISO7498].  This memo interprets a presentation address as an

Rose [Page 5] RFC 1085 ISO Presentation Services December 1988

    ordered-tuple containing:
  1. one or more network addresses
  2. a transport selector
  3. a session selector
  4. a presentation selector
    Each selector is an uninterpreted octet string of possibly zero
    length.  The mechanism proposed in this memo completely ignores
    the values of these selectors.  Note however that the value of the
    presentation selector is preserved by the provider.
    A network address is interpreted as containing three components:
  1. a 32-bit IP address
  1. a set indicating which transport services are available

at the IP address (currently only two members are defined:

         TCP and UDP; as experience is gained, other transport
         services may be added); as a local matter, if a member is
         present it may have an "intensity" associated with it:
         either "possibly present" or "definitely present"
  1. a 16-bit port number
    As a consequence of these interpretations, any application-entity
    residing in the network can be identified by its network address.
    2. Presentation context list
    A list of one or more presentation contexts.  Each presentation
    context has three components:
  1. a presentation context identifier (PCI), an integer
  1. an abstract syntax name, an object identifier
  1. an abstract transfer name, an object identifier
    The range of values these components may take is severely
    restricted by this memo.  In particular, exactly two contexts are
    defined: one for association control and the other for the
    specific application service element which is being carried as ROS
    APDUs (see the section on connection establishment for the precise
    values).
    In addition, if the presentation context list appears in a
    "result" list (e.g., the Presentation context result list

Rose [Page 6] RFC 1085 ISO Presentation Services December 1988

    parameter for the P-CONNECT service), a fourth component is
    present:
  1. an acceptance indicator
    which indicates if the context was accepted by both the service
    provider and the remote peer.  If the context was not accept, a
    brief reason, such as "abstract syntax not supported" is given.
    For the novice reader, one might think of the abstract syntax
    notation as defining the vocabulary of some language, that is, it
    lists the words which can be spoken.  In contrast, the abstract
    transfer notation defines the pronunciation of the language.
    3. User data
    User data passes through the presentation service interface as
    ASN.1 objects (in a locally defined form).  Associated with each
    object is a presentation context identifier.  The PCI
    distinguishes the context for which the data is intended.  The
    range of values the PCI may take is severely restricted by this
    memo.  Exactly one of two contexts must always be used: either the
    value for the ACSE presentation context or the value for the ROSE.
    4. Quality of Service
    Quality of service is a collection of "elements".  Each element
    denotes some characteristics of the communication, e.g., desired
    throughput, and some value in an arbitrary unit of measure.  For
    our purposes, only one quality of service element is interpreted,
    "transport-mapping".  Currently, the "transport-mapping" element
    takes on one of two values: "tcp-based" or "udp-based".  At
    present, the two values may also be referred to as "high-quality"
    or "low-quality", respectively.
    As experience is gained, other values may be added.  These values
    would correspond directly to the new transport services which are
    listed in the network address.
    5. Version of Session Service
    Some application service elements (e.g., the ACSE) invoke
    different procedures based on the (negotiated) version of the
    session service available.  Implementations of this memo always
    indicate that session service version 2 has been negotiated.

Rose [Page 7] RFC 1085 ISO Presentation Services December 1988

6. Choice of Transport Service

 Discussion thus far has centered along the use of the TCP as the
 underlying transport protocol.  However, it has also been noted that
 it may be desirable to permit a quality of service with less
 reliability in order to take advantage of some other characteristic
 of the transport service.
 The introduction of this service has several profound impacts on the
 model, and it is beyond the scope of this memo to enumerate these
 impacts.  However, this memo does propose a mechanism by which such a
 facility is implemented.
 To begin, we use the quality of service parameter for the P-CONNECT
 service to select an underlying transport service.  Only one element
 is currently interpreted, "transport-mapping" which takes the value
 "tcp-based" or "udp-based".  If the value is "tcp-based", then the
 presentation provider will use TCP as the underlying transport
 service. If, however, the value of "transport-mapping" is "udp-
 based", then the presentation provider will use the UDP instead.
 The User Datagram Protocol (UDP) [RFC768] is used to implement the
 udp-based service.  Very few transport-level facilities are placed on
 top of the UDP service, i.e., it is not the intent of this memo to
 "re-invent" the facilities in the TCP.  Hence, It is critical to
 understand that
         low-quality means LOW-QUALITY!
 Because the UDP is a packet-oriented protocol, it is necessary to
 slightly redefine the role of the serialization module.  For the
 serializer, we say that each top-level ASN.1 object placed on the
 input queue will form a single UDP datagram on the output queue which
 is given to the network.  Similarly, for the de-serializer, we say
 that each UDP datagram placed on the input queue from the network
 will form a single top-level ASN.1 object placed on the output queue.
 The term "top-level ASN.1 object" refers, of course, to the protocol
 data units being exchanged by the presentation providers.
 It should be noted that in its current incarnation, this memo permits
 the choice of two different transport protocols, e.g., the TCP or the
 UDP.  However, as experience is gained and as other transport
 protocols are deployed (e.g., the VMTP), then future incarnations of
 this memo will permit these transport protocols to be used.  This is
 a three step process: first, the set of transport services defined
 for the network address is updated; second, a corresponding value is
 added to the range of the quality of service element "transport-
 mapping"; and, third, the following sections of this memo are

Rose [Page 8] RFC 1085 ISO Presentation Services December 1988

 modified accordingly.

7. Connection Establishment

 The Connection Establishment facility consists of one service, the
 P-CONNECT service.

7.1. The P-CONNECT Service

 This service is used to bring two identified application-entities
 into communication.  Its successful use results in a presentation
 connection, with an initial defined context set, being established
 between then.  This connection is available for their subsequent
 communication.  This is a confirmed service whose effects are
 sequenced and non-destructive.
 If the udp-based service is selected, then a presentation connection
 is formed which should be used infrequently and will have minimal
 reliability characteristics.
 For our purposes, the P-CONNECT service:
  1. requests TCP or UDP resources,
  1. builds a fixed defined context set, and
  1. exchanges initial user data.
 Following are the interpretation of and the defaults assigned to the
 parameters of the P-CONNECT service:
    1. Calling Presentation Address
      This is a presentation address.  Although the ISO presentation
      service states that this parameter is mandatory, in practice, a
      local implementation rule may be used to determine an
      "ephemeral" address to use.
    2. Called Presentation Address
      This is a presentation address.  Note that when issuing the P-
      CONNECT.REQUEST primitive, this parameter may contain more than
      one network address.  In the P-CONNECT.INDICATION primitive
      however, only one network address, the one actually used to
      establish the presentation connection, is present.  (Appendix C
      describes a strategy which might be used to determine the actual
      network address).

Rose [Page 9] RFC 1085 ISO Presentation Services December 1988

    3. Responding Presentation Address
      This parameter is identical to the value of the Called
      Presentation Address parameter of the P-CONNECT.INDICATION
      primitive.
    4. Multiple defined Contexts
      Always TRUE.  Note that this parameter is present only in the
      DIS version of the presentation service.
    5. Presentation context definition list
    Two contexts are defined:
    PCI     Abstract Syntax Name            Abstract Transfer Name
    ---     --------------------            ----------------------
     1      specific to the application     "iso asn.1 abstract
                                            transfer"
                                            1.0.8825
     3      "acse pci version 1"            "iso asn.1 abstract
                                            transfer"
            2.2.1.0.0                       1.0.8825
    The abstract syntax and transfer names for the ACSE PCI are for
    use with the DIS version of association control.  If the IS
    version is being used, then this PCI is used instead:
     3      "acse pci version 1"            "asn.1 basic encoding"
            2.2.1.0.1                       2.1.1
    6. Presentation context result list
      Identical to the Presentation context definition list with the
      addition that the acceptance indicator for both contexts is
      "accepted".
    7. Default Context Name
      None.
    8. Default Context Result
      Not applicable.

Rose [Page 10] RFC 1085 ISO Presentation Services December 1988

    9. Quality of Service
      The element "transport-mapping" takes the value "tcp-based" or
      "udp-based".  In the future the range of values may be extended.
    10. Presentation Requirements
      None (the kernel functional unit is always used).
    11. Session Requirements
      Full duplex.
    12. Initial synchronization point serial number
      None.
    13. Initial Assignment of tokens
      None.
    14. Session connection identifier
      Unlike the "real" presentation service, depending on the quality
      of service selected, this parameter may have great significance
      to presentation provider.  Hence, the following format of the
      session connection identifier is mandated by this memo.
      user data:        a local string encoded as a T.61 string
                        using ASN.1, e.g., given string "gonzo":
                        14     05     67   6f   6e   7a   6f
                        tag  length   "g"  "o"  "n"  "z"  "o"
      common data:      a universal time encoding using ASN.1, e.g.,
                        given time "880109170845":
                        17     0c     38   38   30   31   30   ...
                        tag  length   "8"  "8"  "0"  "1"  "0"  ...
      additional data:  any string encoded as a T.61 string using ASN.1
                        (optional)
      As a local convention, the presentation provider may disregard
      the first two octets of each data component for transmission on
      the network as when the session connection identifier is
      represented with ASN.1, the tag and length octets will be added
      anyway.

Rose [Page 11] RFC 1085 ISO Presentation Services December 1988

    15. User Data
      A single ASN.1 object is present, the appropriate A-ASSOCIATE
      PDU, carried in presentation context 3.
    16. Result
      One of the following values: acceptance, user-rejection,
      provider-rejection (transient), or provider-rejection
      (permanent).

8. Connection Termination

 The Connection Termination facility consists of three services, the
 P-RELEASE, P-U-ABORT, and P-P-ABORT services.

8.1. The P-RELEASE Service

 This service provides the service user with access to a negotiated
 release facility.  This service has effects which are sequenced and
 non-destructive.  Either presentation user is permitted to request
 this service.  However, in the event of collision, a provider-
 initiated abort procedure will be invoked.
 If the udp-based service is selected, then any data in transit may be
 discarded.
    For our purposes, the P-RELEASE service:
  1. waits for the serialization module to drain,
  1. sends release user data, and
  1. releases TCP or UDP resources
 Following are the interpretation of and the defaults assigned to the
 parameters of the P-RELEASE service:
    1. Result
      Release accepted.
    2. User data
      A single ASN.1 object is present, the appropriate A-RELEASE PDU,

Rose [Page 12] RFC 1085 ISO Presentation Services December 1988

8.2. The P-U-ABORT Service

 This service can be used by either presentation user to force the
 release of a presentation connection at any time and have the
 correspondent presentation user informed of this termination.  This
 service has effects which are not sequenced with respect to preceding
 service invocations and may be destructive.  It does not require the
 agreement of both service users.
    For our purposes, the P-U-ABORT service:
  1. flushes the serialization module,
  1. sends abort user data, and
  1. releases TCP or UDP resources
 Following are the interpretation of and the defaults assigned to the
 parameters of the P-U-ABORT service:
    1. Presentation context identifier list
      Contained in the ASN.1 objects, if any, that are delivered as
      user data.
    2. User data
      A single ASN.1 object is present, an A-ABORT PDU, carried in
      presentation context 3.

8.3. The P-P-ABORT Service

 This service is the means by which the service provider may indicate
 the termination of the presentation connection for reasons internal
 to the service provider.  This service has effects which are not
 sequenced with respect to preceding service invocations.  The
 execution of this service disrupts any other concurrently active
 service and may thus be destructive.
    For our purposes, the P-P-ABORT service:
  1. flushes the serialization module, and
  1. releases TCP or UDP resources
 Following are the interpretation of and the defaults assigned to the
 parameters of the P-P-ABORT service.

Rose [Page 13] RFC 1085 ISO Presentation Services December 1988

    1. Provider reason
      An integer code detailing why the connection was aborted. Codes
      include, but are not limited to: invalid PPDU parameter,
      unexpected PPDU, unrecognized PPDU, and specified reason.
    2. Abort data
      None.

9. Information Transfer

 Although the Information Transfer facility consists of many services,
 only one, the P-DATA service, is provided by this memo.

9.1. The P-DATA Service

 This services provides the service user with a data transfer
 capability.  This service has effects which are sequenced and non-
 destructive.
 If the udp-based service is selected, then there is an upper-bound on
 the size of the serialized ASN.1 objects which may be transmitted.
 This limit, imposed by the UDP, is 65536 octets.  As a practical
 matter, it is probably a good idea to keep datagrams less than or
 equal to 536 octets in size.
 For our purposes, the P-DATA service:
  1. sends user data
 Following are the interpretation of and the defaults assigned to the
 parameters of the P-DATA service:
    1. User data
      A single ASN.1 object is present, a remote operations APDU,
      carried in presentation context 1.

10. Elements of Procedure

 The service provider is in one of the following states:
         IDLE, WAIT1, WAIT2, DATA, WAIT3, or WAIT4
      The possible events are:
         PS-user         P-CONNECT.REQUEST

Rose [Page 14] RFC 1085 ISO Presentation Services December 1988

                         P-CONNECT.RESPONSE
                         P-RELEASE.REQUEST
                         P-RELEASE.RESPONSE
                         P-DATA.REQUEST
                         P-U-ABORT.REQUEST
         network         TCP closed or errored(*)
                         receive ConnectRequest PDU
                         receive ConnectResponse PDU
                         receive ReleaseRequest PDU
                         receive ReleaseResponse PDU
                         receive UserData(*) or CL-UserData(**) PDU
                         receive user-initiated Abort PDU
                         receive provider-initiated Abort PDU
                         timer expires(**)
      The possible actions are:
         PS-user         P-CONNECT.INDICATION
                         P-CONNECT.CONFIRMATION
                         P-RELEASE.INDICATION
                         P-RELEASE.CONFIRMATION
                         P-DATA.INDICATION
                         P-U-ABORT.INDICATION
                         P-P-ABORT.INDICATION
         network         open TCP(*)
                         close TCP(*)
                         send ConnectRequest PDU
                         send ConnectResponse PDU
                         send ReleaseRequest PDU
                         send ReleaseResponse PDU
                         send UserData(*) or CL-UserData(**) PDU
                         send user-initiated Abort PDU
                         send provider-initiated Abort PDU
                         set timer(**)
         (*)   tcp-based service only
         (**)  udp-based service only

10.1. Elements of Procedure specific to the tcp-based service

 The provider maintains the following information for each
 presentation connection:
  1. a local designator for the PS-user

Rose [Page 15] RFC 1085 ISO Presentation Services December 1988

  1. a local designator for a TCP connection
  1. the state of the connection (e.g., IDLE, WAIT1, and so on)
 Upon receiving an event from the network, the provider finds the
 associated presentation connection.  Matching is done by simply
 comparing local designators for the TCP connection.  Whenever a
 connection remains in or returns to the IDLE state, any associated
 resources, such as an attachment to a local TCP port, are released.
 In the procedures which follow, outgoing PDUs are "placed on the
 input queue for the serializer".  This has a different meaning
 depending on the type of PDU being enqueued.  If the PDU is not an
 abort PDU (user-initiated or provider-initiated), then the PDU is
 simply appended to the input queue regardless of the number of PDUs
 present.  If however, the PDU is an abort PDU, then the provider
 checks the size of the input queue.  If the input queue is non-empty
 or if the serializer is busy transmitting to the network, then the
 abort PDU is discarded, and the serializer is flushed, aborting any
 output to the network in progress.  However, if the input queue is
 empty, then the Abort PDU is appended to the queue, and a small timer
 started.  If the timer expires before the PDU has been serialized and
 transmitted, then the serializer is flushed, aborting any output to
 the network in progress.
 Further, in general, whenever the TCP connection is closed (either
 locally by the provider, or remotely by the network) or has errored,
 the serializer is flushed.  The one exception to this is if a
 ReleaseResponse PDU is being serialized and transmitted to the
 network.  In this case, the provider will not close the TCP
 connection until after the serializer has finished.

10.2. Elements of Procedure specific to the udp-based service

 The provider maintains the following information for each
 presentation connection:
  1. a local designator for the PS-user
  1. the 32-bit IP address and 16-bit UDP port number of the

initiating host

  1. the 32-bit IP address and 16-bit UDP port number of the

responding host

  1. the session connection identifier used to establish the

presentation connection

Rose [Page 16] RFC 1085 ISO Presentation Services December 1988

  1. a local designator for an UDP endpoint
  1. the state of the connection (e.g., IDLE, WAIT1, and so on)
  1. a retransmission counter
 Upon receiving an event from the network, the provider finds the
 associated presentation connection.  Matching is done on the basis of
 addresses, ports, and the session connection identifier (i.e., two
 different presentation connections may differ only in their session
 connection identifier).  If no presentation connection can be found,
 then for the purposes of discussion, it may be assumed that a
 "vanilla" presentation connection is created and initialized to the
 IDLE state.  Further, whenever a connection remains in or returns to
 the IDLE state, any associated resources, such as an attachment to a
 local UDP port, are released.
 In the procedures which follow, outgoing PDUs are "placed on the
 input queue for the serializer".  This means that the ASN.1 object is
 serialized and the resulting sequence of octets is sent as a single
 UDP datagram.

10.3. State Transitions

 Following are the rules for transitioning states.  If an event
 associated with a user-generated primitive is omitted, then it is an
 interface error for the user to issue that primitive in the given
 state.  Each state considers all possible incoming PDUs.
 We assume that for the tcp-based service, that some entity starts a
 passive TCP open.  When the passive open completes, the entity, using
 some local rule, locates a PS-user to be associated with the incoming
 presentation connection.  This presentation connection is then placed
 in the IDLE state.  The entity then continues listening for other
 passive opens to complete.  The mechanisms associated with this
 entity are entirely a local matter, the concept of this listener is
 introduced solely as a modeling artifact.
 Finally, if the udp-based service is selected, then CL-UserData PDUs
 are exchanged by the provider instead of UserData PDUs.
                                  IDLE state
      Event:     P-CONNECT.REQUEST primitive issued
 Based on the quality of service parameter and the list of network
 addresses in the called presentation address parameter, the provider

Rose [Page 17] RFC 1085 ISO Presentation Services December 1988

 selects an address for the use of the presentation connection.  The
 method for making this determination is a local matter.  (Appendix C
 discusses a strategy which might be used.)  For the discussion that
 follows, we assume that a network address supporting the desired
 quality of service has been determined.
 Based on the network address chosen from the called presentation
 address parameter, the provider selects a compatible network address
 from the calling presentation address parameter.  The provider
 attaches itself to the port associated with this network address.
 (By local determination, this address need not be used, and an
 "ephemeral" port may be chosen by the provider.)
 For the tcp-based service, the provider attempts to establish a TCP
 connection to the network address listed in the called presentation
 address.  If the connection can not be established, the P-
 CONNECT.CONFIRMATION(-) primitive is issued with a reason of
 provider-rejection, and the provider remains in the IDLE state.
 Regardless, the user data parameter is placed in a ConnectRequest
 PDU, which is put on the input queue for the serializer.
 For the udp-based service, the provider sets the retransmission
 counter to a small value (e.g., 2), and now starts a small timer.
 Regardless, the provider enters the WAIT1 state.
      Event:     ConnectRequest PDU received
 The provider issues the P-CONNECT.INDICATION primitive and enters the
 WAIT2 state.
      Event:     any other PDU received
 If the PDU is not an Abort PDU, the provider constructs a provider-
 initiated Abort PDU, which is put on the input queue for the
 serializer.  Regardless, the provider remains in the IDLE state.
                                  WAIT1 state
      Event:     P-U-ABORT.REQUEST primitive issued
 The user data parameter is placed in an Abort PDU, which is put on
 the input queue for the serializer.  The provider enters the IDLE
 state.

Rose [Page 18] RFC 1085 ISO Presentation Services December 1988

      Event:     ConnectResponse PDU received
 For the udp-based service, the timer is cancelled.  If the PDU
 indicates rejection, the P-CONNECT.CONFIRMATION(-) primitive is
 issued and the provider enters the IDLE state.  Otherwise, the P-
 CONNECT.CONFIRMATION(+) primitive is issued and the provider enters
 the DATA state.
      Event:     user-initiated Abort PDU received
 The provider issues the P-U-ABORT.INDICATION primitive and enters the
 IDLE state.
      Event:     any other PDU received
 If the PDU not an Abort PDU, the provider constructs a provider-
 initiated Abort PDU, which is put on the input queue for the
 serializer.  Regardless, The provider issues the P-P-ABORT.INDICATION
 primitive and enters the the IDLE state.
      Event:     timer expires
 The provider decrements the retransmission counter.  If the resulting
 value is less than or equal to zero, the provider issues the P-
 CONNECT.CONFIRMATION(-) primitive and enters the IDLE state.
 Otherwise, a ConnectRequest PDU is put on the input queue for the
 serializer, the small timer is started again, and the provider
 remains in the WAIT1 state.
                                  WAIT2 state
      Event:     P-CONNECT.RESPONSE primitive issued
 The user data parameter is placed in a ConnectResponse PDU, which is
 put on the input queue for the serializer.  If the result parameter
 had the value user-rejection, the provider enters the IDLE state.
 Otherwise if the parameter had the value acceptance, the provider
 enters the DATA state.

Rose [Page 19] RFC 1085 ISO Presentation Services December 1988

      Event:     P-U-ABORT.REQUEST primitive issued
 The user data parameter is placed in an Abort PDU, which is put on
 the input queue for the serializer.  The provider enters the IDLE
 state.
      Event:     user-initiated Abort PDU received
 The provider issues the P-U-ABORT.INDICATION primitive and enters the
 IDLE state.
      Event:     any other PDU received
 If the PDU is not an Abort PDU, the provider constructs a provider-
 initiated Abort PDU, which is put on the input queue for the
 serializer.  Regardless, The provider issues the P-P-ABORT.INDICATION
 primitive and enters the the IDLE state.
                                  DATA state
      Event:     P-DATA.REQUEST primitive issued
 The user data parameter is placed in a UserData PDU, which is put on
 the input queue for the serializer.  The provider remains in the DATA
 state.
      Event:     P-RELEASE.REQUEST primitive issued
 The user data parameter is placed in a ReleaseRequest PDU, which is
 put on the input queue for the serializer.
 For the udp-based service, the provider sets the retransmission
 counter to a small value (e.g., 2), and now starts a small timer.
 Regardless, the provider enters the WAIT3 state.
      Event:     P-U-ABORT.REQUEST primitive issued
 The user data parameter is placed in an Abort PDU, which is put on
 the input queue for the serializer.  The provider enters the IDLE
 state.

Rose [Page 20] RFC 1085 ISO Presentation Services December 1988

      Event:     UserData PDU received
 The provider issues the P-DATA.INDICATION primitive and remains in
 the DATA state.
      Event:     ReleaseRequest PDU received
 The provider issues the P-RELEASE.INDICATION primitive, and enters
 the WAIT4 state.
      Event:     user-initiated Abort PDU received
 The provider issues the P-U-ABORT.INDICATION primitive and enters
  the IDLE state.
      Event:     any other PDU received
 If the PDU is not an Abort PDU, the provider constructs a provider-
 initiated Abort PDU, which is put on the input queue for the
 serializer.  Regardless, the provider issues the P-P-ABORT.INDICATION
 primitive and enters the the IDLE state.
                                  WAIT3 state
      Event:     P-U-ABORT.REQUEST primitive issued
 The user data parameter is placed in an Abort PDU, which is put on
 the input queue for the serializer.  The provider enters the IDLE
 state.
      Event:     ReleaseResponse PDU received
 For the udp-based service, the timer is cancelled.  The provider
 issues the P-RELEASE.CONFIRMATION primitive and enters the IDLE
 state.
      Event:     user-initiated Abort PDU received
 The provider issues the P-U-ABORT.INDICATION primitive and enters the
 IDLE state.

Rose [Page 21] RFC 1085 ISO Presentation Services December 1988

      Event:     any other PDU received
 If the PDU is not an Abort PDU, the provider constructs a provider-
 initiated Abort PDU, which is put on the input queue for the
 serializer.  Regardless, the provider issues the P-P-ABORT.INDICATION
 primitive and enters the the IDLE state.
      Event:     timer expires
 The provider decrements the retransmission counter.  If the resulting
 value is less than or equal to zero, the provider constructs a
 provider-initiated Abort PDU, which is put on the input queue for the
 serializer.  It then issues the P-P-ABORT.INDICATION primitive and
 enters the IDLE state.  Otherwise, a ReleaseRequest PDU is put on the
 input queue for the serializer, the small timer is started again, and
 the provider remains in the WAIT3 state.
                                  WAIT4 state
      Event:     P-RELEASE.RESPONSE primitive issued
 The user data parameter is placed in a ReleaseResponse PDU, which is
 put on the input queue for the serializer.  The provider now enters
 the IDLE state.
      Event:     P-U-ABORT.REQUEST primitive issued
 The user data parameter is placed in an Abort PDU, which is put on
 the input queue for the serializer.  The provider now enters the IDLE
 state.
      Event:     user-initiated Abort PDU received
 The provider issues the P-U-ABORT.INDICATION primitive and enters the
 IDLE state.
      Event:     any other PDU received
 If the PDU is not an Abort PDU, the provider constructs a provider-
 initiated Abort PDU, which is put on the input queue for the
 serializer.  Regardless, the provider issues the P-P-ABORT.INDICATION
 primitive and enters the the IDLE state.

Rose [Page 22] RFC 1085 ISO Presentation Services December 1988

11. Directory Services

 Although not properly part of the presentation service, this memo
 assumes and specifies a minimal Directory service capability for use
 by the application-entity.
 The function of the Directory Service Element is to provide two
 mappings: first, a service name is mapped into an application entity
 title, which is a global handle on the service; and, second, the
 application-entity title is mapped onto a presentation address.
 The structure of presentation addresses were defined in Section 5.
 The structure of application-entity titles is less solidly agreed
 upon at the present time.  Since objects of this type are not
 interpreted by the presentation service, this memo does not specify
 their structure.  If the DIS version of association control is being
 used, then use of an OBJECT IDENTIFIER will suffice.  If the IS
 version is being employed, then application-entity titles consist of
 two parts: an application-process title and an application-entity
 qualifier.  It is suggested that the AP-Title use an OBJECT
 IDENTIFIER and that the AE-Qualifier use NULL.
 This memo requires the following mapping rules:
    1.  The service name for an OSI application-entity using the
    mechanisms proposed by this memo is:
            <designator> "-" <qualifier>
    where <designator> is a string denoting either domain name or a
    32-bit IP address, and <qualifier> is a string denoting the type
    of application-entity desired, e.g.,
            "gonzo.twg.com-mgmtinfobase"
    2.  Any locally defined mapping rules may be used to map the
    service designation into an application-entity title.
    3.  The application-entity title is then mapped into a
    presentation address, with uninterpreted transport, session, and
    presentation selectors, and one or more network addresses, each
    containing:
  1. the 32-bit IP address resolved from the <designator> portion

of the service name,

  1. a set indicating which transport services are available

Rose [Page 23] RFC 1085 ISO Presentation Services December 1988

         at the IP address,
  1. the 16-bit port number resolved from the <qualifier>

portion of the service name (using the Assigned Numbers

         document), and
  1. optionally, a presentation selector, which is an

uninterpreted sequence of octets.

 The method by which the mappings are obtained are straight-forward.
 The directory services element employs the Domain Name System along
 with a local table which may be used to resolve the address employing
 local rules.
 In the simplest of implementations, the DNS is used to map the
 <designator> to an IP address, and to fill-in the set of transport
 services available at the IP address.  The port number is found in a
 local table derived from the current Assigned Numbers document.
 Finally, the presentation selector is empty.
 A more ambitious implementation would use a local table to perhaps
 provide a presentation selector.  This would be useful, e.g., in
 "proxy" connections.  The network address would resolve to the proxy
 agent for the non-IP device, and the presentation selector would
 indicate to the proxy agent the particular non-IP device desired.
 This implies, of course, that the local table and the proxy agent
 bilaterally agree as to the interpretation of each presentation
 selector.

12. Remarks

 To begin, if one really wanted to implement ISO applications in a
 TCP/IP-based network, then the method proposed by [RFC1006] is the
 preferred method for achieving this.  However, in a constrained
 environment, where it is necessary to host an application layer
 entity with a minimal amount of underlying OSI infrastructure, this
 memo proposes an alternative mechanism.  It should be noted that an
 OSI application realized using this approach can be moved directly to
 an [RFC1006]-based environment with no modifications.
 A key motivation therefore is to minimize the size of the alternate
 underling infrastructure specified by this memo.  As more and more
 presentation services functionality is added, the method proposed
 herein would begin to approximate the ISO presentation protocol.
 Since this in contrary to the key motivation, featurism must be
 avoided at all costs.

Rose [Page 24] RFC 1085 ISO Presentation Services December 1988

13. Acknowledgements

 Several individuals contributed to the technical quality of this
 memo:
         Karl Auerbach, Epilogue Technologies
         Joseph Bannister, Unisys
         Amatzia Ben-Artzi, Sytek
         Stephen Dunford, Unisys
         Lee Labarre, MITRE
         Keith McCloghrie, The Wollongong Group
         Jim Robertson, Bridge Communications
         Glenn Trewitt, Stanford University

14. References

   [ISO7498]  Information Processing Systems - Open Systems
              Interconnection, "Basic Reference Model", October, 1984.
   [ISO8509]  Information Processing Systems - Open Systems
              Interconnection, " Service Conventions".
   [ISO8650]  Information Processing Systems - Open Systems
              Interconnection, " Protocol Specification for the
              Association Control Service Element (Final Text
              of DIS 8650)", January, 1988.
   [ISO8822]  Information Processing Systems - Open Systems
              Interconnection, " Connection Oriented Presentation
              Service Definition (Final Text of DIS 8822)",
              April, 1988.
   [ISO8823]  Information Processing Systems - Open Systems
              Interconnection, " Connection Oriented Presentation
              Protocol Specification (Final Text of DIS 8822)",
              April, 1988.
   [ISO8824]  Information Processing Systems - Open Systems
              Interconnection, " Specification of Abstract Syntax
              Notation One (ASN.1)", December, 1987.
   [ISO8825]  Information Processing Systems - Open Systems
              Interconnection, "Specification of basic encoding rules
              for Abstract Syntax Notation One (ASN.1)",
              December, 1987.
   [ISO9072/2]  Information Processing Systems - Text Communication
                MOTIS, " Remote Operations Part 2: Protocol

Rose [Page 25] RFC 1085 ISO Presentation Services December 1988

                Specification (Working Document for DIS 9072/2)",
                November, 1987.
   [RFC768]  Postel, J., "User Datagram Protocol", RFC 768, USC/ISI,
             28 August 1980.
   [RFC791]  Postel, J., "Internet Protocol - DARPA Internet Program
             Protocol Specification", RFC 791, USC/ISI,
             September 1981.
   [RFC793]  Postel, J., "Transmission Control Protocol - DARPA
             Internet Program Protocol Specification", RFC 793,
             USC/ISI, September 1981.
   [RFC1006]  Rose, M., and D. Cass, "ISO Transport 1 on Top of the
              TCP Version: 3", Northrop Research and Technology
              Center, May 1987.

Appendix A:

Abstract Syntax Definitions

 RFC1085-PS DEFINITIONS ::=
 BEGIN
 PDUs ::=
         CHOICE {
             connectRequest
                 ConnectRequest-PDU,
             connectResponse
                 ConnectResponse-PDU,
             releaseRequest
                 ReleaseRequest-PDU,
             releaseResponse
                 ReleaseResponse-PDU,
             abort
                 Abort-PDU,
             userData
                 UserData-PDU,
             cL-userData
                 CL-UserData-PDU

Rose [Page 26] RFC 1085 ISO Presentation Services December 1988

         }
  1. - connect request PDU
 ConnectRequest-PDU ::=
     [0]
         IMPLICIT SEQUENCE {
             version[0]          -- version-1 corresponds to to this
                                    memo
                 IMPLICIT INTEGER { version-1(0) },
             reference
                 SessionConnectionIdentifier,
             calling
                 PresentationSelector
                 OPTIONAL,
             called[2]
                 IMPLICIT PresentationSelector
                 OPTIONAL,
             asn[3]              -- the ASN for PCI #1
                 IMPLICIT OBJECT IDENTIFIER,
             user-data
                 UserData-PDU
         }
 SessionConnectionIdentifier ::=
     [0]
         SEQUENCE {
             callingSSUserReference
                 T61String,
             commonReference
                 UTCTime,
             additionalReferenceInformation[0]
                 IMPLICIT T61String
                 OPTIONAL
         }
 PresentationSelector ::=
     [1]
         IMPLICIT OCTET STRING

Rose [Page 27] RFC 1085 ISO Presentation Services December 1988

  1. - connect response PDU
 ConnectResponse-PDU ::=
     [1]
         IMPLICIT SEQUENCE {
             reference           -- present only in the udp-based
                                 -- service
                 SessionConnectionIdentifier
                 OPTIONAL,
             responding
                 PresentationSelector
                 OPTIONAL,
             reason[2]           -- present only if the connection
                                 -- was rejected
                 IMPLICIT Rejection-reason
                 OPTIONAL,
             user-data           -- present only if reason is absent
                                 -- OR has the
                                 -- value rejected-by-responder
                 UserData-PDU
                 OPTIONAL
         }
 Rejection-reason ::=
         INTEGER {
             rejected-by-responder(0)
             called-presentation-address-unknown(1),
             local-limit-exceeded(3),
             protocol-version-not-supported(4),
         }
  1. - release request PDU
 ReleaseRequest-PDU ::=
     [2]
         IMPLICIT SEQUENCE {
             reference           -- present only in the udp-based
                                 -- service
                 SessionConnectionIdentifier
                 OPTIONAL,
             user-data
                 UserData-PDU
         }

Rose [Page 28] RFC 1085 ISO Presentation Services December 1988

  1. - release response PDU
 ReleaseResponse-PDU ::=
     [3]
         IMPLICIT SEQUENCE {
             reference           -- present only in the udp-based
                                 -- service
                 SessionConnectionIdentifier
                 OPTIONAL,
             user-data
                 UserData-PDU
         }
  1. - abort PDU
 Abort-PDU ::=
     [4]
         SEQUENCE {
             reference           -- present only in the udp-based
                                 -- service
                 SessionConnectionIdentifier
                 OPTIONAL,
             user-data   -- MAY BE present on user-initiated abort
                 UserData-PDU
                 OPTIONAL,
             reason[1]   -- ALWAYS present on provider-initiated abort
                 IMPLICIT Abort-reason
                 OPTIONAL
         }
 Abort-reason ::=
         INTEGER {
             unspecified(0),
             unrecognized-ppdu(1),
             unexpected-ppdu(2),
             unrecognized-ppdu-parameter(4),
             invalid-ppdu-parameter(5),
             reference-mismatch(9)
         }
  1. - data PDU
 UserData-PDU ::=
     [5]                         -- this is the ASN.1 object

Rose [Page 29] RFC 1085 ISO Presentation Services December 1988

         ANY                     -- if it is a top-level PDU, it
                                 -- is in PCI #1, otherwise PCI #3
  1. - data PDU for the udp-based service
 CL-UserData-PDU ::=
     [6]
         IMPLICIT SEQUENCE {
             reference
                 SessionConnectionIdentifier,
             user-data[0]                -- this is the ASN.1 object
                 ANY                     -- it is always in PCI #1
         }
 END

Appendix B:

Example of Serialization

 Consider the following call to ROSE:
         RO-INVOKE (operation number      = 5
                    operation class       = synchronous
                    argument              = NONE
                    invocation identifier = 1
                    linked invocation id. = NONE
                    priority              = 0)
             .REQUEST
 Ultimately, ROSE will use the P-DATA service:
         P-DATA (user data = {
                               1,        -- this is the PCI
                               {         -- this is the ASN.1 object
                                  invokeID 1,
                                  operation-value 5,
                                  argument {}
                               }
                             })
             .REQUEST
 The presentation provider will construct a UserData PDU and send this
 via the transport connection:

Rose [Page 30] RFC 1085 ISO Presentation Services December 1988

    [5] {
          {
            1,
            5,
            {}
          }
        }
 Applying the basic encoding rules for ASN.1, we have an stream of 12
 octets.
    a5  0a                                       [5]
    tag len
    a0  08                               [0]
    tag len
    02  01  01           invokeID 1
    tag len value
    02  01  05           operation-value 5
    tag len value
    30  00                       argument NULL
    tag len
 Of course, in actual use, the argument would not be NONE and this
 could be expected to dominate the size of the UserData PDU.  However,
 it is worth nothing that the overhead of the encoding mechanism used
 is on the order of 10 octets, hardly a staggering amount!

Appendix C:

Determination of Network Called Address

 As described in Section 10, when the P-CONNECT.REQUEST primitive is
 issued the presentation provider must determine which of the network
 addresses present in the called presentation address parameter to use
 for the presentation connection.  The first step in this
 determination is to examine the quality of service parameter and
 consider only those network addresses which support the corresponding
 transport service.  In practice, it is likely that each network
 address will support exactly the same transport services, so using
 quality of service as a discriminant will either permit all or none
 or the network addresses present to be selected.  This appendix
 describes a local policy which might be employed when deciding which
 network address to use.
 The policy distinguishes between "underlying failures" and

Rose [Page 31] RFC 1085 ISO Presentation Services December 1988

 "connection establishment failures".  An "underlying failure" occurs
 when, using the desired transport service, the initiating
 presentation provider is unable to contact the responding
 presentation provider.  For the tcp-based service, this means that a
 TCP connection could not be established for some reason.  For the
 udp-based service, it means that a response was not received before
 final time-out.  In contrast, a "connection establishment failure"
 occurs when the responding presentation provider can be contacted,
 but the presentation connection is rejected by either the
 presentation provider or the correspondent presentation user.
 The policy is simple: starting with the first network address
 present, attempt the connection procedure.  If the procedure fails
 due to an "underlying failure", then the next network address in the
 list is tried.  This process is repeated until either an underlying
 connection is established or all network addresses are exhausted.
 If, however, a "connection establishment failure" occurs, then the
 presentation provider immediately indicates this failure to the
 presentation user and no further network addresses are considered.
 Note that this is only one conformant policy of many.  For example,
 the presentation provider may wish to order network addresses based
 on the "intensity" associated with the members present in the set of
 transport services for each network address.

Author's Address:

 Marshall Rose
 The Wollongong Group
 1129 San Antonio Road
 Palo Alto, CA 94303
 Phone: (415) 962-7100
 EMail: mrose@TWG.COM

Rose [Page 32]

/data/webs/external/dokuwiki/data/pages/rfc/rfc1085.txt · Last modified: 1988/12/23 22:03 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki